An anonymous gentleman was kind enough to take some notes during the recent Plantinga/Dennett exchange. It sounds a little disappointing, but I still would have sacrificed my gall-bladder to have been there. Read more here.

Recall my previous discussion of Descartes’ possible version of the replacement argument. Let’s take this premise:

The mind and body do not have the same essential properties.

And modify it slightly to a specific property (if existence is a property at all, which we will just suppose):

Possibly, I exist and my body does not.

If we take it to be true I am a male in every possible world in which I exist (Josh is essentially male), then there are worlds in which I exist and I am a male, but my body does not exist. I don’t know what that means for Josh’s being essentially male, but it seems that either male-ness is either non-essential or it is not an attribute of the body. I don’t know which is true, but it is an interesting fork.

Kripke’s term for an expression that has the same referent in every possibly world. This includes proper names and natural-kinds. Example:

“The 44th president of the United States” designates Barack Obama in the actual world, but it does not rigidly designate him because in some possible world John McCain is the 44th President of the United States. However, “Barack Obama” picks out the same essence in every possible world that “Barack Obama” designates anything at all.

(You can read the context here, but I’m taking the translation from the IEP)

[T]here is a great difference between the mind and the body, inasmuch as the body is by its very nature always divisible, while the mind is utterly indivisible. For when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any parts within myself; I understand myself to be something quite single and complete….By contrast, there is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts; and this very fact makes me understand that it is divisible. This one argument would be enough to show me that the mind is completely different from the body…. (AT VII 86-87: CSM II 59).

The IEP sets up his argument in the following way:

1.I understand the mind to be indivisible by its very nature.
2.I understand body to be divisible by its very nature.
3.Therefore, the mind is completely different from the body.

It doesn’t take much to realize this argument is missing something and is overstating its case. The conclusion does not follow without the following hidden premise:

(HP) If the mind and body have different properties, then they are completely different.

However, I don’t see that premise as true at all. In fact, it is extremely counter-intuitive. But we can mend the argument in a way Descartes would probably object to:

1. The mind has the property of being essentially indivisible.
2. The body is has the property of being essential divisible.
3. If the mind and body are identical, they have the same essential properties.[The law of indescernibility of identicals: x = y → (∀F)(Fx ↔ Fy)]
4. The mind and body do not have the same essential properties [from 1,2]
.: The mind and body are not identical [MT from 3,4]

Trope: An unrepeatable, simple property that stands in contrast with a ‘universal’. Tropes do not exemplify universals like particulars which are complex events, but belong to the subject alone. An example would be the basketball skills of Michael Jordan or Beethoven’s musical talent. It should not be confused with the linguistic speech act that carries the same name.